Any of a class of angiosperm plants having a single cotyledon in the seed. Monocotyledons have leaves with parallel veins, flower parts in multiples of three, and fibrous root systems. Their primary vascular bundles are scattered throughout the stem, not arranged in a ring as in eudicotyledons. Grasses, palms, lilies, irises, and orchids are monocotyledons. See more at leaf. Compare eudicotyledon.